The seller doesn't know what he's talking about. ALL Alembic pickups are low impedance. If you hook them up to the typical passive electronics found in most instruments, there will be very little output. Alembic pickups require a pre-amp, as do all "active" pickups. Some. like EMGs, have the pre-amp built into the pickup casing. Others, like Alembic, wire the pickups to a preamp in the control cavity. Buy these, drop them into a stock Fender, and you're going to be extremely disappointed.

Ibpesq and all...as a point of grammar and description it would as you say best to describe them as low impedance rather than passive..I guess they are all 'passive' until they are hooked up to the pre amps then they become 'active'. Wonder where the filters & pre amps went as you would expect them to be sold as a whole package!